Light-Colored Engineered Wood Boards

ABSTRACT

Light-colored woodbase boards are manufactured from wood fiber bleached and colored with liquid colorant preparations comprising at least one pigment and at least one dye which absorbs in the visible region of the electromagnetic spectrum.

The present invention relates to light-colored woodbase boards manufactured from wood fiber bleached and colored using liquid colorant preparations comprising at least one pigment and at least one dye which absorbs in the visible region of the electro-magnetic spectrum.

The invention also relates to the use of these woodbase boards for producing fittings and to fittings which comprise these woodbase boards.

Within the woodbase materials segment the market for medium-density fiberboard (MDF) and high density fiberboard (HDF) is in a vigorous growth phase. Production volumes have more than tripled within the last decade.

MDF and HDF can be processed in the same way as conventional chipboard. By virtue of their uniform construction, however, they are also suitable for producing profiled parts and are therefore becoming increasingly established in furnituremaking. For example, fittings for rooms and for decorative purposes (in exhibition stand constructions, for example) and also high-quality furniture are already being fabricated from these boards and coated with overlay or simply given a colorless varnish so that the woodlike structure remains visible.

By their very nature these boards, depending on the type of wood used, have a more or less pronounced brown coloration, which is of low esthetic value for application in the furniture segment.

Mass coloring with the pigment and dye preparations known from WO-A-04/35276 allows the intrinsic coloring of the wood fiber to be compensated in the area of dark hues and at high depths of shade. This allows colorful, fully through-colored, lightfast MDF boards to be obtained which as a result are of high esthetic value and are suitable for manufacturing articles with a long life, such as domestic furniture.

Woodbase boards, especially MDF boards, having bright light hues (L*≧75) even at high depths of shade, being colored yellow or orange, for example, or with a low depth of shade, i.e., lightened pastel hues, a neutral gray for example, have not, however, been disclosed to date. Boards of this kind would nevertheless be of particular interest for the manufacture of furniture and interior decoration articles, for kitchens or bathrooms, for example.

JP-A-55-164142 describes chipboard panels manufactured from woodchips which to start with have been oxidatively bleached with sodium chloride and then colored using a direct dye. Bleaching there is performed in order to enhance the capacity for the woodchips to be colored right through, and strong colors are said to be produced.

Finally, in DE-A-10 2004 050 278, unpublished at the priority date of the present specification, light to white woodbase boards are described which are manufactured from bleached wood fiber and/or mass-colored with a white pigment.

It was an object of the invention, therefore, to provide light-colored woodbase boards.

Found accordingly have been light-colored woodbase boards manufactured from wood fiber bleached and colored using liquid colorant preparations comprising pigment and dye.

A feature of the woodbase boards of the invention are their clean light hues. These hues may be “soft” pastel hues blended with white, which can be obtained by coloring in a standard depth of shade of ≦ 1/9, in particular of ≦ 1/25, or strong hues with luminance L*≧75.

The woodbase boards of the invention are, for example, MDF or HDF boards or chipboard. MDF boards are particularly preferred.

MDF and HDF boards are typically manufactured in a continuous operation: Washed, water-moist, finely chopped wood pieces (chips) are first preheated to approximately 80° C. and then softened in a digester under a pressure of 2 to 5 bar at a temperature of 100 to 150° C. In the downstream refiner the chips are then fiberized. The refiner consists of two metal disks with a radial relief which rotate close to one another in opposite directions. The fibers leave the refiner via the blowline. Here, generally, the glue is applied. Binders used are typically urea-formaldehyde resins, in some cases reinforced with melamine, or, for moisture-resistant boards, urea-melamine-formaldehyde resins. Isocyanates as well are in use as binders. The binders are generally applied together with the desired additives (e.g., curing agent, paraffin dispersion, colorants) to the fibers. The fibers to which glue has been applied then run through a drier, in which they are dried to moisture contents of 8% to 15% by weight. In certain cases glue is not applied to the dried fibers until subsequently, in special, continuously operating mixers.

In chipboard manufacture the glue is applied to the pre-dried chips in continuous mixers.

The fibers or chips to which glue has been applied are then poured to form mats, subjected to cold precompaction if appropriate, and pressed in heated presses at temperatures of 170 to 240° C. to form boards.

Serving as base material for the woodbase boards of the invention may be, in principle, any fibrous materials obtainable from plants. Thus, for example, in addition to the wood fibers typically employed, fibers obtainable from palms are suitable. Preferred base materials are light wood varieties, particularly spruce or pine, although darker wood varieties, such as beech, can also be used.

No distinction is made below between the terms “wood fibers” and “chips”; instead, the term “wood fibers” is intended to comprise “chips” as well.

The wood fiber used in the woodbase boards of the invention is bleached.

The chemical bleaching of wood fiber involves the color-imparting impurities in the wood being destroyed or rendered ineffective by means of oxidizing and/or reducing chemicals. Suitable examples for oxidative bleaching include hydrogen peroxide, ozone, oxygen, salts of halogen oxo acids, such as chlorites, and salts of organic and inorganic peracids, such as peracetates, percarbonates, and perborates, especially their alkali metal salts, particularly sodium salts, preference being given to the percarbonates and hydrogen peroxide. Examples of those suitable for reductive bleaching include reductive sulfur compounds, such as dithionites, disulfites, sulfites or sulfur dioxide, sulfinic acids and their salts, particularly the alkali metal salts, and especially the sodium salts, and hydroxy carboxylic acids, such as citric acid and malic acid. Preferred reducing agents are the disulfites and sulfites, especially sodium hydrogensulfite, and also malic acid and citric acid.

Particularly preferred wood fiber for the woodbase boards of the invention is fiber which has been bleached first oxidatively and then reductively.

With very particular preference the oxidative bleaching is carried out with percarbonates or hydrogen peroxide and the reductive bleaching with sulfites or with malic or citric acid.

An advantageous bleaching procedure involves treating 5% to 40% by weight wood fiber dispersions continuously in countercurrent towers at temperatures of 90 to 150° C. and pressures of up to 3 bar with aqueous solutions or dispersions of the bleaches. Operation takes place typically in the presence of complexing agents, such as EDTA, in order to prevent the bleaches being degraded by transition metal ions.

Particularly when manufacturing MDF/HDF boards of the invention, fiber bleaching can be performed, advantageously, during board manufacture. The bleaches may be added to the chips in the preheater or in the refiner. Complexing agents are also added with preference.

After bleaching, the wood fiber used in the woodbase boards of the invention is colored using liquid colorant preparations which comprise at least one pigment and at least one dye which absorbs in the visible region of the electromagnetic spectrum.

These colorant preparations generally comprise 0.01% to 10% by weight, preferably 0.5% to 10% by weight, of dye, based on the pigment.

With particular preference these colorant preparations comprise

-   (A) 10% to 70% by weight of at least one pigment, -   (B) 0.05% to 7% by weight of at least one dye which absorbs in the     visible region of the electromagnetic spectrum, -   (C) 1% to 50% by weight of at least one dispersant, -   (D) 10% to 88.95% by weight of water or of a mixture of water and at     least one water retainer, and -   (E) 0 to 5% by weight of further typical colorant preparation     ingredients.

As component (A) organic or inorganic pigments may be comprised in the colorant preparations. It will be appreciated that the colorant preparations may also comprise mixtures of different organic or different inorganic pigments, or mixtures of organic and inorganic pigments.

The pigments are preferably in finely divided form and accordingly have, typically, average particle sizes of 0.1 to 5 μm, in particular 0.1 to 3 μm, and especially 0.1 to 1 μm.

The organic pigments are typically organic chromatic pigments and black pigments. Inorganic pigments may likewise be color pigments (chromatic, black, and white pigments) and also luster pigments.

Examples of suitable organic color pigments include the following

-   -   monoazo pigments:         -   C.I. Pigment Brown 25;         -   C.I. Pigment Orange 5, 13, 36, 38, 64, and 67;         -   C.I. Pigment Red 1, 2, 3, 4, 5, 8, 9, 12, 17, 22, 23, 31,             48:1, 48:2, 48:3, 48:4, 49, 49:1, 51:1, 52:1, 52:2, 53,             53:1, 53:3, 57:1, 58:2, 58:4, 63, 112, 146, 148, 170, 175,             184, 185, 187, 191:1, 208, 210, 245, 247, and 251;         -   C.I. Pigment Yellow 1, 3, 62, 65, 73, 74, 97, 120, 151, 154,             168, 181, 183, and 191;         -   C.I. Pigment Violet 32;     -   disazo pigments:         -   C.I. Pigment Orange 16, 34, 44, and 72;         -   C.I. Pigment Yellow 12, 13, 14, 16, 17, 81, 83, 106, 113,             126, 127, 155, 174, 176, 180, and 188;     -   disazo condensation pigments:         -   C.I. Pigment Yellow 93, 95, and 128;         -   C.I. Pigment Red 144, 166, 214, 220, 221, 242, and 262;         -   C.I. Pigment Brown 23 and 41;     -   anthanthrone pigments:         -   C.I. Pigment Red 168;     -   anthraquinone pigments:         -   C.I. Pigment Yellow 147, 177, and 199;         -   C.I. Pigment Violet 31;     -   anthrapyrimidine pigments:         -   C.I. Pigment Yellow 108;     -   quinacridone pigments:         -   C.I. Pigment Orange 48 and 49;         -   C.I. Pigment Red 122, 202, 206, and 209;         -   C.I. Pigment Violet 19;     -   quinophthalone pigments:         -   C.I. Pigment Yellow 138;     -   diketopyrrolopyrrole pigments:         -   C.I. Pigment Orange 71, 73, and 81;         -   C.I. Pigment Red 254, 255, 264, 270, and 272;     -   dioxazine pigments:         -   C.I. Pigment Violet 23 and 37;         -   C.I. Pigment Blue 80;     -   flavanthrone pigments:         -   C.I. Pigment Yellow 24;     -   indanthrone pigments:         -   C.I. Pigment Blue 60 and 64;     -   isoindoline pigments:         -   C.I. Pigment Orange 61 and 69;         -   C.I. Pigment Red 260;         -   C.I. Pigment Yellow 139 and 185;     -   isoindolinone pigments:         -   C.I. Pigment Yellow 109, 110, and 173;     -   isoviolanthrone pigments:         -   C.I. Pigment Violet 31;     -   metal complex pigments:         -   C.I. Pigment Red 257;         -   C.I. Pigment Yellow 117, 129, 150, 153, and 177;         -   C.I. Pigment Green 8;     -   perinone pigments:         -   C.I. Pigment Orange 43;         -   C.I. Pigment Red 194;     -   perylene pigments:         -   C.I. Pigment Black 31 and 32;         -   C.I. Pigment Red 123, 149, 178, 179, 190, and 224;         -   C.I. Pigment Violet 29;     -   phthalocyanine pigments:         -   C.I. Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, and 16;         -   C.I. Pigment Green 7 and 36;     -   pyranthrone pigments:         -   C.I. Pigment Orange 51;         -   C.I. Pigment Red 216;     -   pyrazoloquinazolone pigments:         -   C.I. Pigment Orange 67;         -   C.I. Pigment Red 251;     -   thioindigo pigments:         -   C.I. Pigment Red 88 and 181;         -   C.I. Pigment Violet 38;     -   triarylcarbonium pigments:         -   C.I. Pigment Blue 1, 61, and 62;         -   C.I. Pigment Green 1;         -   C.I. Pigment Red 81, 81:1, and 169;         -   C.I. Pigment Violet 1, 2, 3, and 27;         -   C.I. Pigment Black I (aniline black);     -   C.I. Pigment Yellow 101 (aldazine yellow);     -   C.I. Pigment Brown 22.

Examples of suitable inorganic color pigments include:

-   white pigments: titanium dioxide (C.I. Pigment White 6), zinc white,     pigment-grade zinc oxide; zinc sulfide, lithopone; -   black pigments: black iron oxide (C.I. Pigment Black 11), iron     manganese black, spinel black (C.I. Pigment Black 27); carbon black     (C.I. Pigment Black 7); -   chromatic pigments: chromium oxide, chromium oxide hydrate green,     chromium green (C.I. Pigment Green 48); cobalt green (C.I. Pigment     Green 50); ultramarine green;     -   cobalt blue (C.I. Pigment Blue 28 and 36; C.I. Pigment Blue 72);         ultramarine blue; manganese blue;     -   ultramarine violet; cobalt violet and manganese violet;     -   red iron oxide (C.I. Pigment Red 101); cadmium sulfoselenide         (C.I. Pigment Red 108); cerium sulfide (C.I. Pigment Red 265);         molybdate red (C.I. Pigment Red 104); ultramarine red;     -   brown iron oxide (C.I. Pigment Brown 6 and 7), mixed brown,         spinel phases and corundum phases (C.I. Pigment Brown 29, 31,         33, 34, 35, 37, 39, and 40), chromium titanium yellow (C.I.         Pigment Brown 24), chromium orange;     -   cerium sulfide (C.I. Pigment Orange 75);     -   yellow iron oxide (C.I. Pigment Yellow 42); nickel titanium         yellow (C.I. Pigment Yellow 53; C.I. Pigment Yellow 157, 158,         159, 160, 161, 162, 163, 164, and 189); chromium titanium         yellow; spinel phases (C.I. Pigment Yellow 119); cadmium sulfide         and cadmium zinc sulfide (C.I. Pigment Yellow 37 and 35);         chromium yellow (C.I. Pigment Yellow 34); bismuth vanadate (C.I.         Pigment Yellow 184).

The luster pigments are platelet-shaped pigments of single-phase or multiphase construction whose color play is marked by the interplay of interference, reflection, and absorption phenomena. Examples include aluminum platelets and aluminum, iron-oxide, and mica platelets bearing one or more coats, especially of metal oxides.

The colorant preparations generally comprise 10% to 70% by weight, preferably 10% to 60% by weight, of pigment (A).

As component (B) the colorant preparations comprise at least one dye which absorbs in the visible region of the electromagnetic spectrum and is from the group of the cationic dyes, the anionic dyes, and the disperse dyes. Particularly suitable dyes are those which are soluble in water or in a water-miscible or water-soluble organic solvent. The dyes (B) employed preferably have a hue which is comparable in each case to that of the pigments (A), since in this way it is possible to achieve particularly intense coloration of the woodbase boards, even with light hues. An alternative is to use dyes (B) which differ in hue, thereby enabling the coloration to be shaded.

Suitable dyes are, in particular, cationic dyes, anionic dyes, and disperse dyes. Very particularly suitable dyes are direct dyes and disperse dyes.

Suitable cationic dyes (B) belong in particular to the di- and triarylmethane, xanthene, azo, cyanine, azacyanine, methine, acridine, safrazine, oxazine, indoline, nigrosin, and phenazine range, with dyes from the azo, triarylmethane, and xanthene ranges being preferred.

Specific examples that may be recited include the following: C.I. Basic Yellow 1, 2, and 37; C.I. Basic Orange 2; C.I. Basic Red 1 and 108; C.I. Basic Blue 1, 7, and 26; C.I. Basic Violet 1, 3, 4, 10, 11, and 49; C.I. Basic Green 1 and 4; C.I. Basic Brown 1 and 4.

Cationic dyes (B) may also be colorants comprising external basic groups. Suitable examples here are C.I. Basic Blue 15 and 161.

Useful cationic dyes (B) further include the corresponding dye bases in the presence of solubilizing acidic agents. Examples include the following: C.I. Solvent Yellow 34; C.I. Solvent Orange 3; C.I. Solvent Red 49; C.I. Solvent Violet 8 and 9; C.I. Solvent Blue 2 and 4; C.I. Solvent Black 7.

Particularly suitable anionic dyes are compounds containing sulfonic acid groups and originating from the azo, anthraquinone, metal complex, triarylmethane, xanthene, and stilbene ranges, with dyes from the triarylmethane, azo, and metal complex (especially copper complex, chromium complex, and cobalt complex) range being preferred.

Specific examples include the following: C.I. Acid Yellow 3, 19, 36, 59, 119, and 204; C.I. Acid Orange 7, 8, 44, 74, 92, and 142; C.I. Acid Red 52, 88, 159, 351, and 357; C.I. Acid Violet 17, 46, 56, 58, 65, and 90; C.I. Acid Blue 9, 193, and 199; C.I. Acid Brown 355; C.I. Acid Black 52 and 194; C.I. Direct Yellow 4 and 11; C.I. Direct Red 80, 81, and 254; C.I. Direct Violet 35 and 51; C.I. Direct Blue 47, 67, 199, 267, and 279.

These dyes are water-soluble particularly when they are in the form of the alkali metal salt, especially lithium, sodium or potassium salt, or in the form of an unsubstituted or substituted ammonium salt, especially an alkanolammonium salt.

Disperse dyes are employed preferably in the form of commercially available aqueous dispersions and display their coloring action in the woodbase board manufacturing operation by means of diffusion at high temperatures.

Particularly suitable examples include disperse dyes from the range of the quinophthalones and anthraquinones.

The colorant preparations comprise dye (B) generally in amounts of 0.5% to 10% by weight, preferably 1% to 8% by weight, based in each case on the pigment (A). Based on the total weight of the preparation this corresponds to amounts of in general 0.05% to 7% by weight, in particular 0.1% to 5.6% by weight.

Preferred pigment/dye combinations for light hues are, for example: C.I. Pigment Orange 34 and C.I. Direct Yellow 11; C.I. Pigment Yellow 74 and C.I. Direct Yellow 4.

Pure light pastel hues are obtainable in particular by blending white pigments, especially C.I. Pigment White 6, with shaded color pigments, e.g., C.I. Pigment Black 7 and C.I. Basic Violet 3. Light gray shades can advantageously also be obtained by shading the white pigment with appropriate dyes, examples being blue dyes, such as C.I. Direct Blue 47, 67, 267, and 279, and/or violet dyes, such as C.I. Direct Violet 35 and 51, and if appropriate, yellow dyes, such as C.I. Direct Yellow 4. The fraction of the white pigment here is in each case typically 80% to 99% by weight, based on the total amount of colorant.

At least one dispersant is comprised as component (C) in the colorant preparations.

Particularly suitable dispersants (C) are nonionic and anionic water-soluble surface-active additives.

Particularly suitable nonionic additives (C) are based on polyethers (additives (C1)).

Besides the unmixed polyalkylene oxides, preferably C₂-C₄ alkylene oxides and phenyl-substituted C₂-C₄ alkylene oxides, especially polyethylene oxides, polypropylene oxides, and poly(phenylethylene oxide)s, suitability here is possessed in particular by block copolymers, especially polymers containing polypropylene oxide blocks and polyethylene oxide blocks, or poly(phenylethylene oxide) blocks and polyethylene oxide blocks, and also random copolymers of these alkylene oxides.

The polyalkylene oxides may be prepared by polyaddition of the alkylene oxides to starter molecules, such as to saturated or unsaturated aliphatic and aromatic alcohols, phenol or naphthol, which may each be substituted by alkyl, especially C₁-C₁₂ alkyl, preferably C₄-C₁₂ or C₁-C₄ alkyl, to saturated or unsaturated aliphatic and aromatic amines, or to saturated or unsaturated aliphatic carboxylic acids and carboxamides. Typically 1 to 300 mol, preferably 3 to 150 mol, of alkylene oxide are used per mole of starter molecule.

Suitable aliphatic alcohols generally comprise 6 to 26 carbon atoms, preferably 8 to 18 carbon atoms, and may be unbranched, branched or cyclic in structure. Examples that may be mentioned include octanol, nonanol, decanol, isodecanol, undecanol, dodecanol, 2-butyloctanol, tridecanol, isotridecanol, tetradecanol, pentadecanol, hexadecanol (cetyl alcohol), 2-hexyldecanol, heptadecanol, octadecanol (stearyl alcohol), 2-heptylundecanol, 2-octyidecanol, 2-nonyltridecanol, 2-decyltetradecanol, oleyl alcohol, and 9-octadecanol, and mixtures of these alcohols, such as C₈/C₁₀, C₁₃/C₁₅ and C₁₅/C₁₈ alcohols, and cyclopentanol and cyclohexanol. Of particular interest are the saturated and unsaturated fatty alcohols obtained by fat hydrolysis and reduction from natural raw materials, and the synthetic fatty alcohols from the oxo process. The alkylene oxide adducts with these alcohols typically have average molecular weights M_(n) of 200 to 5000.

Examples of the abovementioned aromatic alcohols, besides unsubstituted phenol and α- and β-naphthol include hexylphenol, heptylphenol, octylphenol, nonylphenol, isononylphenol, undecylphenol, dodecylphenol, di- and tributylphenol, and dinonylphenol.

Suitable aliphatic amines are in accordance with the aliphatic alcohols recited above. Particular importance here as well is possessed by the saturated and unsaturated fatty amines which have preferably 14 to 20 carbon atoms. Examples of aromatic amines include aniline and its derivatives.

Suitable aliphatic carboxylic acids are, in particular, saturated and unsaturated fatty acids comprising preferably 14 to 20 carbon atoms, hydrogenated, part-hydrogenated, and unhydrogenated resin acids, and polybasic carboxylic acids, dicarboxylic acids for example, such as maleic acid.

Suitable carboxamides are derived from these carboxylic acids.

As well as the alkylene oxide adducts with the monofunctional amines and alcohols, very particular interest attaches to the alkylene oxide adducts with at least difunctional amines and alcohols.

Preferred at least difunctional amines are amines with a functionality of two to five which conform in particular to the formula H₂N—(R¹—NR²)_(n)—H(R¹: C₂-C₆ alkylene, R²: hydrogen or C₁-C₆ alkyl; n: 1 to 5). Specific examples include the following: ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, propylene-1,3-diamine, dipropylenetriamine, 3-amino-1-ethyleneaminopropane, hexamethylenediamine, dihexamethylenetriamine, 1,6-bis(3-aminopropylamino)-hexane, and N-methyldipropylenetriamine, particular preference being given to hexamethylenediamine and diethylenetriamine, and very particular preference to ethylenediamine.

These amines are preferably reacted first with propylene oxide and then with ethylene oxide. The ethylene oxide content of the block copolymers is typically about 10% to 90% by weight.

The block copolymers based on polyfunctional amines generally have average molecular weights M_(n) of 1000 to 40000, preferably 1500 to 30000.

Preferred at least difunctional alcohols are alcohols having a functionality of two to five. Examples that may be mentioned include C₂-C₆ alkylene glycols and the corresponding dialkylene and polyalkylene glycols, such as ethylene glycol, 1,2- and 1,3-propylene glycol, 1,2- and 1,4-butylene glycol, 1,6-hexylene glycol, dipropylene glycol and polyethylene glycol, glycerol, and pentaerythritol, particular preference being given to ethylene glycol and polyethylene glycol and very particular preference to propylene glycol and dipropylene glycol.

Particularly preferred alkylene oxide adducts with at least difunctional alcohols have a central polypropylene oxide block, i.e., are based on a propylene glycol or polypropylene glycol which is initially reacted with further propylene oxide and then with ethylene oxide. The ethylene oxide content of the block copolymers is typically 10% to 90% by weight.

The block copolymers based on polyhydric alcohols generally have average molecular weights M_(n) of 1000 to 20000, preferably 1000 to 15000.

Alkylene oxide block copolymers of this kind are known and are available commercially, for example, under the names Tetronic® and Pluronic® (BASF).

Examples that may be mentioned of the water-soluble anionic surface-active agents particularly suitable for use as component (C) include additives based on polymers of ethylenically unsaturated carboxylic acids (C2), additives based on polyurethanes (C3), and additives based on acidic phosphoric, phosphonic, sulfuric and/or sulfonic esters of the abovementioned polyethers (C4).

It will be appreciated that mixtures of two or more additives (C) may also be used, hence including mixtures of different nonionic additives and mixtures of different anionic additives, and also mixtures of nonionic and anionic additives.

Particularly suitable anionic water-soluble surface-active additives based on polymers of unsaturated carboxylic acids (C2) are additives from the group of the homopolymers and copolymers of ethylenically unsaturated monocarboxylic acids and/or ethylenically unsaturated dicarboxylic acids, which may further comprise, in copolymerized form, vinyl monomers not comprising acid function; the alkoxylation products of these homopolymers and copolymers; and the salts of these homopolymers and copolymers and their alkoxylation products.

Examples that may be mentioned of the carboxyl-containing monomers and the vinyl monomers include the following:

-   -   acrylic acid, methacrylic acid, and crotonic acid;     -   maleic acid, maleic anhydride, maleic monoesters, maleic         monoamides, reaction products of maleic acid with diamines that         may have been oxidized to derivatives containing amine oxide         groups, and fumaric acid, of which maleic acid, maleic         anhydride, and maleic monoamides are preferred;     -   styrenics, such as styrene, methylstyrene, and vinyltoluene;         ethylene, propylene, isobutene, diisobutene, and butadiene;         vinyl ethers, such as polyethylene glycol monovinyl ether; vinyl         esters of linear or branched monocarboxylic acids, such as vinyl         acetate and vinyl propionate; alkyl esters and aryl esters of         ethylenically unsaturated monocarboxylic acids, especially         acrylic and methacrylic esters, such as methyl, ethyl, propyl,         isopropyl, butyl, pentyl, hexyl, 2-ethylhexyl, nonyl, lauryl,         and hydroxyethyl(meth)acrylate and also phenyl, naphthyl, and         benzyl (meth)acrylate; dialkyl esters of ethylenically         unsaturated dicarboxylic acids, such as dimethyl, diethyl,         dipropyl, diisopropyl, dibutyl, dipentyl, dihexyl,         di-2-ethyl-hexyl, dinonyl, dilauryl, and di-2-hydroxyethyl         maleate and fumarate; vinyl-pyrrolidone; acrylonitrile and         methacrylonitrile, preference being given to styrene, isobutene,         diisobutene, acrylic esters, and polyethylene glycol monovinyl         ether.

Particular examples of preferred homopolymers of these monomers are polyacrylic acids.

The copolymers of the stated monomers may be synthesized from two or more, especially three different monomers. Random copolymers, alternating copolymers, block copolymers, and graft copolymers may be present. Preferred copolymers include styrene/acrylic acid, acrylic acid/maleic acid, acrylic acid/methacrylic acid, butadiene/acrylic acid, isobutene/maleic acid, diisobutene/maleic acid, and styrene/maleic acid copolymers, each of which may comprise acrylic esters and/or maleic esters as additional monomer constituents.

The carboxyl groups of the nonalkoxylated homopolymers and copolymers are at least partly present, preferably, in salt form, in order to ensure solubility in water. Suitable salts are, for example, the alkali metal salts, such as sodium and potassium salts, and the ammonium salts.

The nonalkoxylated polymeric additives (C2) typically have average molecular weights M_(w) of 900 to 250000. The molecular weight ranges particularly suitable for the individual polymers depend, of course, on their composition. Molecular weight indications are given below by way of example for different polymers: polyacrylic acids: M_(w) of 900 to 250000; styrene/acrylic acid copolymers: M_(w) of 1000 to 50000; acrylic acid/methacrylic acid copolymers: M_(w) of 1000 to 250000; acrylic acid/maleic acid copolymers: M_(w) of 2000 to 70000.

Besides these homopolymers and copolymers themselves their alkoxylation products are also of particular interest as additives (C2).

By these products are meant in accordance with the invention, in particular, the polymers which have been partly to (where possible) fully esterified with polyether alcohols. The degree of esterification of these polymers is generally 30 to 80 mol %.

Particularly suitable for the esterification are the polyether alcohols themselves, preferably polyethylene glycol and polypropylene glycols, and also their derivatives with endgroup capping at one end, particularly the corresponding monoethers, such as monoaryl ethers, monophenyl ethers for example, and especially mono-C₁-C₂₆ alkyl ethers, examples being ethylene glycols and propylene glycols etherified with fatty alcohols, and the polyetheramines which are preparable, for example, by converting a terminal OH group of the corresponding polyether alcohols or by polyaddition of alkylene oxides with preferably primary aliphatic amines. Preference is given in this context to polyethylene glycols, polyethylene glycol monoethers, and polyetheramines. The average molecular weights M_(n) of the polyether alcohols and their derivatives that are used are typically 200 to 10000.

By controlling the ratio of polar to nonpolar groups it is possible to tailor the surface-active properties of the additives (C2).

Anionic surface-active additives (C2) of this kind are likewise known and available commercially, for example, under the names Sokalan® (BASF), Joncryl® (Johnson Polymer), Alcosperse® (Alco), Geropon® (Rhodia), Good-Rite®D (Goodrich), Neoresin® (Avecia), Orotan® and Morez® (Rohm & Haas), Disperbyk® (Byk), and also Tegospers® (Goldschmidt).

As anionic surface-active additives the pigment preparations of the invention may further comprise polyurethane-based additives (C3).

The term “polyurethane” is intended in accordance with the invention to refer not only to the pure reaction products of polyfunctional isocyanates (C3a) with organic compounds comprising isocyanate-reactive hydroxyl groups (C3b) but also the reaction products additionally functionalized through the addition of further isocyanate-reactive compounds, such as of carboxylic acids bearing primary or secondary amino groups, for example.

These additives score over other surface-active additives in their low ion conductivity and their neutral pH.

Suitable polyfunctional isocyanates (C3a) for preparing the additives (C3) include, in particular, diisocyanates, although compounds having three or four isocyanate groups may also be employed. Both aromatic and aliphatic isocyanates can be used.

Examples that may be recited of preferred di- and triisocyanates include the following: tolylene 2,4-diisocyanate (2,4-TDI), diphenylmethane 4,4′-diisocyanate (4,4′-MDI), para-xylylene diisocyanate, 1,4-diisocyanatobenzene, tetramethylxylylene diisocyanate (TMXDI), diphenylmethane 2,4′-diisocyanate (2,4′-MDI) and triisocyanatotoluene, and also isophorone diisocyanate (IPDI), 2-butyl-2-ethylpentamethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2-bis(4-isocyanatocyclohexyl)propane, trimethylhexane diisocyanate, 2-isocyanatopropylcyclohexyl isocyanate, 2,4,4- and 2,2,4-trimethylhexamethylene diisocyanate, methylenebis(cyclohexyl) 2,4′-diisocyanate, cis-cyclohexane 1,4-diisocyanate, trans-cyclohexane 1,4-diisocyanate, and 4-methylcyclohexane 1,3-diisocyanate (H-TDI).

It will be appreciated that mixtures of isocyanates (C3a) can also be used. By way of example mention may be made here of the following: mixtures of structural isomers of tolylene 2,4-diisocyanate and triisocyanatotoluene, e.g., mixtures of 80 mol % tolylene 2,4-diisocyanate and 20 mol % tolylene 2,6-diisocyanate; mixtures of cis- and trans-cyclohexane 1,4-diisocyanate; and mixtures of tolylene 2,4- or 2,6-diisocyanate with aliphatic diisocyanates, such as hexamethylene diisocyanate and isophorone diisocyanate.

Preferred suitable isocyanate-reactive organic compounds (C3b) are compounds having at least two isocyanate-reactive hydroxyl groups per molecule. Also suitable as compound (C3b), however, are compounds containing only one isocyanate-reactive hydroxyl group per molecule. These monofunctionalized compounds may replace in whole or in part the compounds comprising at least two isocyanate-reactive hydroxyl groups per molecule in the context of reaction with the polyisocyanate (C3a).

Listed below are examples of particularly preferred isocyanate-reactive compounds (C3b) having at least two isocyanate-reactive hydroxyl groups per molecule.

These are polyetherdiols, polyesterdiols, lactone-based polyesterdiols, diols and triols with up to 12 carbon atoms, dihydroxy carboxylic acids, dihydroxy sulfonic acids, dihydroxy phosphonic acids, polycarbonate diols, polyhydroxy olefins, and polysiloxanes having on average at least two hydroxyl groups per molecule.

Examples of suitable polyether diols (C3b) are homopolymers and copolymers of C₂-C₄ alkylene oxides, such as ethylene oxide, propylene oxide and butylene oxide, tetra-hydrofuran, styrene oxide and/or epichlorohydrin, Which are obtainable in the presence of a suitable catalyst, boron trifluoride for example. Polyether diols additionally suitable are obtainable by (co)polymerization of these compounds in the presence of a starter having at least two acidic hydrogen atoms, such as water, ethylene glycol, thioglycol, mercaptoethanol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,12-dodecanediol, ethylenediamine, aniline or 1,2-di-(4-hydroxyphenyl)propane.

Examples of particularly suitable polyether diols (C3b) are polyethylene glycol, polypropylene glycol, polybutylene glycol, and polytetrahydrofuran, and also copolymers thereof.

The molecular weight M_(n) of the polyether diols is preferably 250 to 5000, more preferably 500 to 2500.

Polyesterdiols (hydroxy polyesters) suitable as isocyanate-reactive compound (C3b) are general knowledge.

Preferred polyesterdiols (C3b) are the reaction products of diols with dicarboxylic acids or their reactive derivatives, examples being anhydrides or dimethyl esters.

Suitable dicarboxylic acids are saturated and unsaturated, aliphatic and aromatic dicarboxylic acids, which may bear additional substituents, such as halogen. Preferred aliphatic dicarboxylic acids are saturated unbranched α,ω-dicarboxylic acids comprising 3 to 22, especially 4 to 12 carbon atoms.

Examples of particularly suitable dicarboxylic acids are the following: succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecane-dicarboxylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydro-phthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, terephthalic acid, dimethyl terephthalate, and dimethyl isophthalate.

Particularly suitable diols are saturated and unsaturated, aliphatic and cycloaliphatic diols. The particularly preferred aliphatic α,ω-diols are unbranched and have 2 to 12, especially 2 to 8, especially 2 to 4 carbon atoms. Preferred cycloaliphatic diols derive from cyclohexane.

Examples of particularly suitable diols are the following: ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 2-methylpropane-1,3-diol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, cis- and trans-but-2-ene-1,4-diol, 2-butyne-1,4-diol, and cis- and trans-1,4-di(hydroxymethyl)cyclohexane.

The molecular weight M_(n) of the polyesterdiols is preferably 300 to 5000.

Lactone-based polyesterdiols suitable as isocycanate-reactive compound (C3b) are based in particular on aliphatic saturated unbranched ω-hydroxycarboxylic acids having 4 to 22, preferably 4 to 8, carbon atoms. Also suitable are branched co-hydroxy-carboxylic acids in which one or more —CH₂— groups in the alkylene chain have been replaced by —CH(C₁-C₄ alkyl)-.

Examples of preferred co-hydroxycarboxylic acids are γ-hydroxybutyric acid and δ-hydroxyvaleric acid.

It will be appreciated that the abovementioned diols are also suitable as isocyanate-reactive compounds (C3b), the preferences applicable being the same as those above.

Likewise suitable as isocyanate-reactive compounds (C3b) are triols having in particular 3 to 12, especially 3 to 8, carbon atoms. An example of a particularly suitable triol is trimethylolpropane.

Dihydroxycarboxylic acids suitable as isocyanate-reactive compounds (C3b) are, in particular, aliphatic saturated dihydroxycarboxylic acids comprising preferably 4 to 14 carbon atoms. Especial suitability is possessed by dihydroxycarboxylic acids of the formula

in which A¹ and A² are identical or different C₁-C₄ alkylene radicals and R is hydrogen or C₁-C₄ alkyl.

A particularly preferred example of these dihydroxycarboxylic acids is dimethylolpropionic acid (DMPA).

Further suitable as isocyanate-reactive compounds (C3b) of the corresponding dihydroxysulfonic acids and dihydroxyphosphonic acids, such as 2,3-dihydroxy-propanephosphonic acid.

The term “dihydroxycarboxylic acid” is also intended here to comprise compounds comprising more than one carboxyl function (or anhydride or ester function). Such compounds are obtainable by reacting dihydroxy compounds with tetracarboxylic dianhydrides, such as pyromellitic dianhydride or cyclopentanetetracarboxylic dianhydride, in a polyaddition reaction in a molar ratio of 2:1 to 1.05:1, and have preferably an average molecular weight M_(n) of 500 to 10000.

Examples of suitable polycarbonate diols (C3b) include the reaction products of phosgene with an excess of diols, especially unbranched saturated aliphatic α,ω-diols having 2 to 12, especially 2 to 8, in particular 2 to 4 carbon atoms.

Polyhydroxy olefins with isocyanate-reactive compound (C3b) suitability are, in particular, α,ω-dihydroxy olefins, preference being given to α,ω-dihydroxybutadienes.

The polysiloxanes further suitable as isocyanate-reactive compound (C3b) comprise on average at least two hydroxyl groups per molecule. Particularly suitable polysiloxanes contain on average 5 to 200 Si atoms (number average) and are substituted in particular by C₁-C₁₂ alkyl groups, especially methyl groups.

Examples of isocyanate-reactive compounds (C3b) containing only one isocyanate-reactive hydroxyl group include, in particular, aliphatic, cycloaliphatic, araliphatic or aromatic monohydroxycarboxylic and -sulfonic acids.

The polyurethane-based additives (C3) are prepared by reacting compounds (C3a) and (C3b), the molar ratio of (C3a) to (C3b) being typically 2:1 to 1:1, preferably 1.2:1 to 1:1.2.

It is possible, in addition to the aforementioned isocyanate-reactive compounds (C3b), to add further compounds having isocyanate-reactive groups, examples being dithiols, thioalcohols, such as thioethanol, amino alcohols, such as ethanolamine, and N-methylethanolamine, or diamines, such as ethylenediamine, and so prepare polyurethanes which in addition to the urethane groups also carry isocyanurate groups, allophanate groups, urea groups, biuret groups, uretdione groups or carbodiimide groups. Further examples of isocyanate-reactive compounds of this kind are aliphatic, cycloaliphatic, araliphatic or aromatic carboxylic acids and sulfonic acids which carry at least two primary and/or secondary amino groups.

It will be appreciated that corresponding compounds containing only one isocyanate-reactive group, examples being monoalcohols, primary and secondary monoamines, monoamino carboxylic and sulfonic acids, and mercaptans, can also be added. Typical quantities used are up to 10 mol %, based on (C3a).

At least some of the carboxyl groups of the reaction products (C3) are preferably in salt form in order to ensure solubility in water. Suitable examples are alkali metal salts, such as sodium and potassium salts, and ammonium salts.

The additives (C3) typically have average molecular weights M_(w) of 500 to 250000.

By controlling the ratio of polar to nonpolar groups it is possible to tailor the surface-active properties of the additives (C3).

Anionic surface-active additives (C3) of this kind are known and are available commercially under the name Borchi® GEN SN95 (Borchers), for example.

Water-soluble anionic surface-active additives based on acidic phosphoric, phosphonic, sulfuric and/or sulfonic esters of polyethers (C4) are based in particular on the reaction products of the above-recited polyethers (C1) with phosphoric acid, phosphorus pentoxide, and phosphonic acid or sulfuric acid and sulfonic acid. In these cases the polyethers are converted into the corresponding phosphoric monoesters or diesters and phosphonic esters or the sulfuric monoesters and sulfonic esters. These acidic esters are preferably in the form of water-soluble salts, especially alkali metal salts, in particular sodium salts, and ammonium salts, but may also be used in the form of the free acids.

Preferred phosphates and phosphonates derive in particular from alkoxylated, especially ethoxylated, fatty alcohols and oxo alcohols, alkylphenols, fatty amines, fatty acids, and resin acids; preferred sulfates and sulfonates are based in particular on alkoxylated, especially ethoxylated, fatty alcohols, alkylphenols, and amines, including polyfunctional amines, such as hexamethylenediamine.

Anionic surface-active additives of this kind are known and are available commercially, for example, under the names Nekal® (BASF), Tamol® (BASF), Crodafos® (Croda), Rhodafac® (Rhodia), Maphos® (BASF), Texapon® (Cognis), Empicol® (Albright & Wilson), Matexil® (ICI), Soprophor® (Rhodia), and Lutensit® (BASF).

The colorant preparations typically have a dispersant (C) content of 1% to 50% by weight, in particular of 1% to 40% by weight.

Water forms the liquid vehicle of the colorant preparations.

The liquid phase of the colorant preparations is preferably a mixture of water and a water retainer. Serving as water retainers are, in particular, organic solvents which are of low evaporability (i.e., which generally have a boiling point >100° C.), hence their water retention effect, and which are soluble in water or miscible with water.

Examples of suitable water retainers are polyhydric alcohols, preferably unbranched and branched polyhydric alcohols having 2 to 8, especially 3 to 6, carbon atoms, such as ethylene glycol, 1,2- and 1,3-propylene glycol, glycerol, erythritol, pentaerythritol, pentitols, such as arabitol, adonitol and xylitol, and hexitols, such as sorbitol, mannitol, and dulcitol. Additionally suitable, for example, are di-, tri-, and tetraalkylene glycols and their mono(especially C₁-C₆, particularly C₁-C₄)alkyl ethers. By way of example mention may be made of di-, tri-, and tetraethylene glycol, diethylene glycol monomethyl, monoethyl, monopropyl, and monobutyl ether, triethylene glycol monomethyl, monoethyl, monopropyl, and monobutyl ether, di-, tri-, and tetra-1,2- and -1,3-propylene glycol, and di-, tri-, and tetra-1,2- and -1,3-propylene glycol monomethyl, monoethyl, monopropyl, and monobutyl ether.

The colorant preparations generally comprise 10% to 88.95% by weight, preferably 10% to 80% by weight, of liquid phase (D). Where water is in a mixture with a water-retaining organic solvent, said solvent accounts generally for 1% to 80% by weight, preferably 1% to 60% by weight, of phase (D).

As component (E) the colorant preparations may further comprise typical adjuvants, such as biocides, defoamers, antisettling agents, and rheological modifiers, whose proportion may in general amount to up to 5% by weight.

The colorant preparations may be obtained in a variety of ways. It is preferred first to prepare a pigment dispersion to which the dye is then added in solid or, in particular, dissolved form or in a form in which it is dispersed in liquid phase, especially aqueous phase.

The colorant preparations may be added to the mixture of wood fiber and/or wood chips and binders, serving as the basis for the woodbase boards of the invention, this addition being possible in various ways and at various points in the manufacturing operation. In the case of the preferred MDF/HDF boards they are introduced advantageously via the blowline, separately from or together with the glue, directly in the board manufacturing operation.

EXAMPLES Production of Inventive MDF Boards Example 1 a) Bleaching

In a 5-l vessel with anchor stirrer and thermostat-controlled heating, 70 g of wood fiber (pine) and 1 g of ethylenediaminetetraacetic acid (Trilon® B, BASF) in 3 l of water were heated to 70° C. with stirring. Following the addition of 7 g of sodium percarbonate the batch was stirred at 70-75° C. for 1 h. Then 7 g of sodium dithionite were added, with final stirring at 70-75° C. for a further 30 min.

The pulp slurry was cooled to room temperature, the liquid constituents were separated off on a 1 mm mesh sieve, and the product was washed briefly under running water and rolled out thoroughly. The filtered material, after spreading, was then dried at 60° C. in a forced-air drying oven for 3 days.

b) Coloring

The bleached wood fiber was mixed thoroughly in a paddle mixer and sprayed with the glue batch indicated in the table below, which comprised a gray pigment preparation with the composition likewise indicated therein.

TABLE Pigment preparation C.I. Pigment White 6 59.0% by weight C.I. Pigment Black 7  5.0% by weight C.I. Basic Violet 3  0.4% by weight Dispersant 20.0% by weight Water 15.6% by weight Glue batch Urea-melamine-formaldehyde resin, 100.0 parts by weight 69% by weight in water Paraffin dispersion, 60% by weight in  4.1 parts by weight water Pigment preparation  19.7 parts by weight Water  49.2 parts by weight Solid resin content of the liquor 45% Solid resin/bone-dry fiber 14% Liquor per 100 kg bone-dry fiber  31.1 kg

The fibers with glue applied were then poured to form a mat, which was subjected to cold precompaction and pressed to a board at 190° C.

For comparison, an MDF board was manufactured from unbleached wood fiber in a procedure which was otherwise unchanged.

In both cases a pale gray MDF board was obtained. The MDF board manufactured for comparison, however, had a yellowish brownish gray shade, whereas the inventive MDF board manufactured from bleached wood fiber had a clean, lighter gray shade (luminance difference ΔL* as against the comparison board: 2).

Example 2

A pilot MDF plant was fed with pinechips and the MDF production operation was commenced with a throughput of 21 kg/h. Immediately upstream of the refiner a 20% strength by weight aqueous sodium dithionate solution, corresponding to 5% of sodium dithionate on bone-dry fiber, was pumped into the operation.

The resultant bleached wood fibers were sprayed continuously through the blowline with the glue batch indicated in table 2, which composed a gray pigment preparation with the composition likewise indicated therein.

TABLE 2 Glue batch Urea-melamine-formaldehyde resin, 100.0 parts by weight 66.5% by weight in water Paraffin dispersion, 60% by weight in  4.0 parts by weight water Aqueous pigment preparation comprising  47.5 parts by weight 65% by weight C.I. Pigment White 6 0.6% by weight C.I. Direct Blue 267 0.3% by weight C.I. Direct Violet 51 0.1% by weight C.I. Direct Yellow 4 7% by weight dispersant Water  21.4 parts by weight Solid resin content of the liquor 44% Solid resin/bone-dry fiber 14% Liquor per 100 kg bone-dry fiber  31.8 kg

The glued wood fibers were dried in the downstream continuous dryer to a residual moisture content of about 9% by weight and then poured in batches to form mats, which were each subjected to cold precompaction and pressed to a 16 mm board at 190° C. with a pressing time factor of 15 s/mm.

In comparison with an MDF board produced without bleaching but by otherwise the same procedure, the resulting luminance difference ΔL* was 3 units. 

1. A light-colored woodbase board manufactured from wood fiber bleached and colored using a liquid colorant preparation comprising at least one pigment and at least one dye which absorbs in the visible region of the electromagnetic spectrum.
 2. The woodbase board according to claim 1, wherein the wood fiber is bleached first oxidatively and then reductively.
 3. The woodbase board according to claim 1, wherein the wood fiber is colored with a colorant preparation comprising 0.01% to 10% by weight of dye, based on the pigment.
 4. The woodbase board according to claim 1, wherein the wood fiber is colored with a colorant preparation comprising (A) 10% to 70% by weight of at least one pigment, (B) 0.05% to 7% by weight of at least one dye which absorbs in the visible region of the electromagnetic spectrum, (C) 1% to 50% by weight of at least one dispersant, (D) 10% to 88.95% by weight of water or of a mixture of water and at least one water retainer, and (E) 0 to 5% by weight of further typical colorant preparation ingredients.
 5. The woodbase board according to claim 1, wherein the wood fiber is colored in a standard depth of shade of ≦ 1/9 with said colorant preparation.
 6. The woodbase board according to claim 1, wherein the wood fiber is colored with a colorant preparation having a CIELAB luminance L*≧75.
 7. The woodbase board according to claim 1, which is an MDF or HDF board or chipboard.
 8. (canceled)
 9. A fitting comprising the woodbase board according to any of claim
 1. 